The invention has been developed in connection with the very large conveyor belts used in Alberta to transport tar sand from a mine to a bitumen recovery plant. Therefore the invention and the problems which it seeks to alleviate are described below with respect to this particular application; however, it is to be understood that the invention is not limited to said application.
The tar sand conveyor belts are large and operate in demanding conditions. They commonly have a width of 60 inches and may stretch in length over a distance of several hundred feet or several miles, depending on their role in the system. In use, a stream of tar sand is continuously dropped onto the endless belt at the loading point, to form a furrow about 55 inches in width and 12 inches in height. The stream usually includes large boulders and, in winter, chunks of frozen tar sand. Some of these pieces with hundreds or thousands of pounds and, in some cases, they are dropped onto the belt from a height of several feet. As a result, the belts frequently experience deep cuts and impact stress. In addition, the hydrocarbons present in the tar sand tend to permeate the material of the belt and cause deterioration.
In structure, each belt comprises a bottom layer of rubber, a series of steel cables laid lengthwise in parallel, closely spaced arrangement on top of the bottom layer, and a top layer of rubber laid over the cables. The three components are bonded together by a middle layer of vulcanized tie-gum rubber.
Each conveyor is formed of one or more supported lengths of belt. In the case of a conveyor made using only a single length of belt, the ends of the length are joined to form an endless belt running on idlers and around two end rolls. In the case of a longer conveyor, the ends of several lengths are joined in sequence in end to end relation to form the endless belt. Furthermore, when a belt fails, it is usual to cut out a short length at the failure point and splice in a substitute length of new material. So each belt includes one or more joins or splices along its length.
As previously mentioned, the belts are subjected to stress and chemical attack--thus they periodically fail. These failures commonly occur at the splices.
Heretofore the conventional practice for joining the belt ends involved the following: the top layer of rubber would be cut away at the splice zone to expose the cable ends. These ends would be scrupulously cleaned. An end portion of the bottom layer would be cut away. Then the bottom rubber layer ends would be brought into abutment and the cable ends laid in side-by-side overlapping relation. Tie-gum would then be applied to cover the splice zone, a section of top rubber would be laid on, and the whole would be vulcanized.
It will be perceived from the foregoing that the connection means between the steel cable ends in a joint of this kind is only the tie-gum rubber, supported by the top and bottom layers of rubber. As mentioned, this is where failure occurs.
The cost is high for repairing such a failure. The failure point is frequently high off the ground. The weather is often cold. Thus it is frequently necessary to first build a heated shelter high off the ground over the splice area. The splicing procedure itself is slow going and labor intensive. But most important, the belt is out of operation for 2 or 3 days. In the case of a 125,000 BOPD synthetic crude plant, the shutdown of a belt can reduce the volume of feed to the plant by 25%, which translates into a loss of many thousands of dollars per day.
One solution to this problem would be to develop a mechanical connector to join the cable ends. Such a connector preferably should have the following characteristics:
(1) a high order of strength; PA1 (2) compactness, as the closely spaced cables each will include such a connector at the splice and they must all fit without problem within a limited area; PA1 (3) a limited degree of flexibility, to enable the connector to negotiate the passage over the end rolls without serious problems; and PA1 (4)lengthwise adjustability to permit the cables to be pre-tensioned to about the same extent.